1. Field of the Invention
The present invention relates to a solid electrolytic capacitor and a method for manufacturing the solid electrolytic capacitor and more particularly to a lower-face electrode type solid electrolytic capacitor having electrode terminals directly drawn on a mounted electrode face of a substrate and the method for manufacturing the same.
2. Description of the Related Art
Conventionally, a solid electrolytic capacitor employing tantalum, niobium, or a like as a valve metal, owing to its small-sized configuration, its large electrostatic capacitance, and its excellent frequency characteristic, is widely used in a decoupling circuit of a CPU (Central Processing Unit), power circuit, or a like. Also, as a portable-type electronic device develops, commercialization of the lower-face electrode type solid electrolytic capacitor, in particular, is in progress.
When the lower-face electrode type solid electrolytic capacitor of this type is to be mounted on an electronic circuit substrate, not only a terminal portion of a substrate mounted electrode face of the lower-face electrode type solid capacitor but also a terminal portion called a “solder fillet” mounted on the side of the lower-face electrode type solid electrolytic capacitor becomes an important factor.
The reason for the above is that quality of mounting connection of the capacitor or a like can be confirmed by observing presence or absence of solder existing beside the fillet after a soldering process is completed since there is a fear of the inconvenience that an electrolytic capacitor is mounted in an inclined state if solder does not wet up equally both on anode and cathode sides, for example, when the solder being molten on a fillet forming face wets up.
To resolve the inconvenience of this kind, a lower-face electrode type solid electrolytic capacitor having a configuration in which a plating process is performed in a terminal portion (on fillet forming face) where a soldering fillet is formed is disclosed (see, for example, Patent References 1[Japanese Patent Application Laid-open No. 2001-52961] and 2 [Japanese Patent Application Laid-open No. 2004-228424]). In the configurations of the disclosed solid electrolytic capacitor, since the plating process is performed on the fillet forming face, the wetting-up of solder is improved, however, there is a disadvantage in manufacturing processes that, after the cutting of a converting substrate or electrode terminal of a lead frame, or a like, the plating process is required on the fillet forming face, thus causing the addition and complication of processes, increase in costs, or a like.
To resolve the disadvantage in manufacturing processes as above, a lower-face electrode type solid electrolytic capacitor having a configuration in which a concave portion is formed on an electrode terminal and a plating processed face is formed in the concave portion to form a fillet forming face (see Patent References 3 [Japanese Patent Application Laid-open No. 2005-101418] and 4 [Japanese Patent Application Laid-open No. 2005-197457]). FIGS. 12A, 12B, and 12C are diagrams showing the lower-face mounted electrolytic type solid electrolytic capacitor 70 disclosed in the Patent Reference 4 and FIG. 12A is a side view showing an anode side of the solid electrolytic capacitor 70, FIG. 12B is an internal perspective view from its front, and FIG. 12C is a side view showing a cathode side of the solid electrolytic capacitor 70. The reference number 71 shows a capacitor element, the number 72 shows an anode lead line, the number 73 shows an anode terminal of a lower-face electrode type solid electrolytic capacitor 70, the number 74 shows a cathode terminal of the lower-face electrode type solid electrolytic capacitor 70, the number 76a shows a plated fillet forming face on its anode side, the number 76b shows a plated fillet forming face on its cathode side, the number 79 is an appropriately -shaped section on its anode side, the number 77 shows an insulating resin employed therein, the number 78 shows a section on its cathode side, the number 99 shows a sheathing resin employed therein, and the number 80 shows a conductive adhesive employed therein. In the FIG. 12B, the dotted portion shows the concave portion on an inner face of which a plating process is performed and one face of which is the fillet forming face 76a and another face of which is the fillet forming face 76b. 
These processes are described by referring to FIGS. 13 and 14. FIG. 13 is a process flow diagram disclosed in the Patent Reference 3. In FIG. 13, Step S61 shows a process of forming a leadframe, Step S62 shows a process of plating the leadframe, Step S63 shows a process of bonding and securing the capacitor element 71 to the leadframe, Step S64 shows a process of forming a mold using the sheathing resin 99, Step S65 shows a process of cutting the sheathing resin 99 and leadframe. A state in which the capacitor element 71 is bonded to the leadframe and the mold is formed using the sheathing resin 99 is shown in FIG. 14. In FIG. 14, the reference number 81 shows a leadframe anode terminal forming portion, the number 82 shows a leadframe cathode terminal forming portion, the numbers 83a and 83b are cutting planes, the numbers 84a and 84b show concave portions serving as fillet forming faces after being cut. Thus, according to the Patent References 3 and 4, by forming a concave portion (dotted portion) processed by plating, the process of the plating following the cutting process is made unnecessary.
However, the disclosed technologies have problems in that the formation of the concave portion of electrode terminals within outer dimensions of the lower-face electrode type solid electrolytic capacitor is required which causes a difficulty in the improvement of volume efficiency of the capacitor element and it is made difficult to stably form fillet forming faces to be used for cutting in the concave portion in which solder is formed.
In the lower-face electrode type solid electrolytic capacitor in which its minimization is required, to achieve further minimization, the improvement of volume efficiency of the capacitor element relative to the outer dimensions of the lower-face electrode type solid electrolytic capacitor is indispensable. However, in the conventional method as shown in FIG. 12 in which concave and convex portions are formed in the leadframe using a throttling process or a like and fillet forming faces 76a and 76b processed by plating are formed in the concave and convex portions, the formation of the plated fillet forming faces 76a and 76b within the outer dimensions of the lower-face electrode type solid electrolytic capacitor is required. This conventional method presents problems. That is, in order to obtain such the plated fillet forming faces 76a and 76b, it is necessary to accept some additional increases in volume and, as a result, the improvement of volume efficiency of the lower-face electrode type solid electrolytic capacitor is blocked and another problem arises that stable formation of the fillet forming face due to the cutting of the concave portion is made difficult.